1. Field of the Invention
This invention relates to a control device suitable for use in a radio communication apparatus employed in a radio communication system using a time-division multiple access method.
2. Description of the Related Art
FIG. 1 is a block diagram showing the structure of a mobile station using a mobile radiotelephone system as a conventional radio communication apparatus, which is disclosed in, for example, the technical journal issued by Mitsubishi Electric Corp., Vol. 60, No. 10, p.p. 55-59, 1986. In the same drawing, there are shown a transmitting and receiving antenna 1, an antenna sharing unit 2 provided to transmit waves and receive them by a single antenna, a transmitting unit 3 for performing modulation and amplification of a transmission signal, a frequency synthesizer 4 for oscillating necessary frequencies, a receiving unit 5 for demodulating signals in a predetermined band, a control unit 6 for controlling respective units, a base-band signal processing unit 7 for processing sound signals, a microphone 8, and a speaker 9. FIG. 2 is a block diagram showing the structure of the control unit 6 constructed by a microcomputer. In the same drawing, there are shown a CPU 10, a RAM 11 from which data are read and in which the data are written, a ROM 12 in which a program is stored, a timer circuit 13, input/output ports (hereinafter called "I/O ports") 141 to 146 for interfacing to the outside, and a bus 16.
The operation of the control unit 6 will now be described. The CPU 10 is operated in accordance with the program stored in the ROM 12. More specifically, the CPU 10 supplies necessary control signals to the transmitting unit 3, the frequency synthesizer 4, the receiving unit 5 (these are collectively called "a radio unit", and a unit, which is related to the transmission, in the radio unit will hereinafter called "a radio transmitting unit"), and the base-band signal processing unit 7 through the I/O ports 141 to 146, and receives necessary information from them. When the time control is required while they are being controlled by the CPU 10, the CPU 10 causes the timer circuit 13 to produce a timer interrupt signal thereby performing the real-time control in accordance with the timer interrupt signal. When it is desired to treat a transmitting-unit start signal (hereinafter called "TXON") for example, output ports each of which has been allotted to the TXON are rendered active during a predetermined period of time after radio channels are allotted. As soon as the radio communication is terminated, the output ports are thereafter rendered inactive during the predetermined period of time.
The CPU 10 supplies the control signals such as TXON, etc. to the radio unit through the I/O ports 141 to 146 in the above-described manner. Thus, when the radio communication is made in accordance with a frequency division multiple access system (hereinafter called "FDMA system"), the operation of the radio unit is made regularly and hence the radio unit is activated without any problem under the above control of the CPU 10. However, when the radio communication is carried out in accordance with a time division multiple access system (hereinafter called "TDMA system") like, for example, the following mobile radiotelephone system (standard number IS-54) which has been discussed at the TIA in U.S.A., the operation of the radio communication apparatus is made intermittently. More specifically, as shown in FIG. 3, the transmission and reception must be performed only with respect to time slots allotted in one TDMA frame. FIG. 3 shows one example in which tri-multiple TDMA system is adopted. Therefore, if the TXON is taken as an example, it is necessary to output a TXON according to the time slots allotted in the TDMA frame as shown in FIG. 4.
The control device suitable for use in the conventional radio communication apparatus (hereinafter called merely "control device") is constructed as described above. Therefore, the control device is accompanied by the problem that since the CPU 10 directly performs the input/output control of the control signal, the control signal required to be inputted and/or outputted in the form of a microsecond order cannot be inputted and/or outputted in the accurate timing even when the timer interrupt operations are often used where the radio communication is made by the TDMA system. Even when the control device activated at high speed as the CPU 10 or other peripheral circuit is used, a problem arises in that the power consumption is increased and the control device becomes expensive.